Field of the Invention
The present invention relates to an image sensor and an imaging method and, more particularly, to a gradation process of an image signal.
Description of the Related Art
In recent years, an ultra high definition video image represented by a 4K resolution image has generally been used and a technique regarding an 8K UHDTV (8K Ultra High Definition Television) has also remarkably been developed. Also in an imaging apparatus, in addition to a request for realization of the large number of pixels and a high frame rate in the related art, a request for realizing 10 or more bits by increasing an information amount per pixel is also increasing.
To realize such requests, it is necessary that an image signal which is output from an image sensor is A/D converted (analog/digital converted) into a multibit digital image signal largely exceeding 10 bits within a predetermined time which is restricted by a frame period or the like. It is also necessary that the A/D converted multibit digital image signal is transmitted to an image processing unit of an imaging apparatus within a predetermined time.
As a unit for transmitting the A/D converted multibit digital image signal to the image processing unit, for example, a high speed differential serial transmission system such as LVDS (Low Voltage Differential signaling) or the like is used. At this time, in order to transmit the multibit digital image signal to the image processing unit within a predetermined time, it is necessary to improve a transmission band width by raising a transmitting frequency or increasing the number of transmission pins. Or, it is necessary that an amount of data which is transmitted is reduced by compressing the multibit digital image signal or the like.
For example, Japanese Patent Application Laid-Open No. 2011-119868 discloses an imaging apparatus having: a compressing unit for reversible-compressing a video signal which was output from an image sensor; an expanding unit for expanding the compressed video signal; and a synthesizing unit for synthesizing the expanded video signal to one frame image. According to such a technique, by reversible-compressing the multibit digital image signal, an amount of data which is transmitted to an image processing unit of the imaging apparatus can be reduced.
However, in order to transmit such a multibit digital image signal that the number of bits is larger than that in the related art to the image processing unit, since it is necessary to raise a transmitting frequency or increase the number of transmission pins, the apparatus becomes an imaging apparatus in which costs are high and a manufacturing difficulty is high. Even in the case of compressing the multibit digital image signal like a technique as disclosed in Japanese Patent Application Laid-Open No. 2011-119868, a scale of a circuit for the compressing process using space information or time information between frames is large and, further, the expanding process in the image processing unit is indispensable, the costs of the imaging apparatus are eventually high.